SELECT inst.* from dir_courses AS cTable JOIN
dir_inst_tut_courses AS instc ON cTable.table_id= instc.course_table_id
JOIN dir_institutes AS inst ON inst.table_id= instc.inst_table_id
WHERE cTable.table_id='507'
AND inst.inst_city_id='184' GROUP BY inst.table_id ORDER BY rand() LIMIT 5